Of course, after each completed transaction you can rate the user who sold you the item. You can give him/her stars on a scale from 1 to 5 and add a comment to the rating.
Remember that the other side of the transaction can reply to your rating.
In LESS_ you can not remove received or submitted ratings by yourself. If for any reason you do not agree with a rating you have received, you can report it to us at email@example.com